NEW YORK — The managing clerk of a high-profile New York City law firm and a Morgan Stanley stockbroker were charged in an insider trading scheme that used notes scribbled on napkins — then eaten to maintain secrecy — to bring in almost $6 million in illicit profits, authorities said Wednesday.

Steven Metro stole insider information from the law offices of Simpson Thacher & Bartlett and passed it on to a friend who became a cooperating witness, according to federal prosecutors in Newark, N.J. The cooperating witness would then divulge the information to Vladimir Eydelman, a stockbroker who worked at Oppenheimer & Co. and then at Morgan Stanley, authorities said.

FBI agents arrested Metro, 40, of Katonah, N.Y., and Eydelman, 42, of Colts Neck, N.J., on Wednesday. Metro’s attorney, James Froccaro Jr., said his client would be entering a not guilty plea “and looks forward to being vindicated at trial.”

William Silverman, a lawyer for Eydelman, did not return a message seeking comment.

Authorities said the scheme began in 2009. They said Metro repeatedly obtained inside information regarding anticipated corporate mergers and acquisitions on which his firm was working. They said he would arrange to meet the cooperating witness at a Manhattan coffee shop to pass on the inside information, which included the stock exchange ticker symbol of the company in which to invest.

The cooperating witness would write the information on a small piece of paper or napkin, prosecutors said. The witness would then meet with Eydelman near the clock at Grand Central Terminal to give him the stolen information, prosecutors said.

The cooperating witness would show Eydelman the napkin or piece of paper with the ticker symbol, they said. Eydelman would memorize the ticker symbol and the cooperating witness would put the paper into his mouth and chew it, they said.

Metro and Eydelman are charged with conspiracy to commit securities fraud, securities fraud and tender offer fraud, and face lengthy prison sentences and large fines. The Securities and Exchange Commission also charged the two with insider trading on Wednesday.

Simpson Thacher has offices around the world and employs more than 850 lawyers. The firm was founded in 1884, and deals with mergers and acquisitions and other financial matters.

In a statement, the company said it had no knowledge of any wrongdoing or charges until Wednesday, and that Metro had been terminated from his position. The charges “are deeply disturbing and unprecedented in our long history,” the firm said, adding that it was reviewing its system of internal controls to see if they could be strengthened.

While this is embarrassing for the firm, the incident shouldn’t do any real harm to it, said Stephen Crimmins, partner at the K&L Gates law firm in Washington, D.C., and a former deputy chief litigation counsel in the SEC’s enforcement division.

People know that a firm like Simpson Thacher has controls in place to protect confidentiality, but no system can control for everything, he said.

“There’s no system that can protect against greed and stupidity,” he said.